Deposition of Ta- or Nb-doped high-k films

ABSTRACT

Methods and compositions for depositing high-k films are disclosed herein. In general, the disclosed methods utilize precursor compounds comprising Ta or Nb. More specifically, the disclosed precursor compounds utilize certain ligands coupled to Ta and/or Nb such as 1-methoxy-2-methyl-2-propanolate (mmp) to increase volatility. Furthermore, methods of depositing Ta or Nb compounds are disclosed in conjunction with use of Hf and/or Zr precursors to deposit Ta-doped or Nb-doped Hf and/or Zr films, The methods and compositions may be used in CVD, ALD, or pulsed CVD deposition processes.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S.Non-provisional application Ser. No. 12/099,027, filed Apr. 7, 2008,which claims the benefit of U.S. Provisional Application No. 60/910,522,filed Apr. 6, 2007, each being incorporated herein by reference in itsentirety for all purposes.

BACKGROUND

1. Field of the Invention

This invention relates generally to the field of semiconductorfabrication. More specifically, the invention relates to compositionsand methods for semiconductor film deposition of Ta or Nb doped high-kmaterials.

2. Background of the Invention

With the dramatic shrinkage in new semiconductor based-devices, one ofthe most concerning issues of scaling metal-oxide-semiconductor fieldeffect transistors (MOSFETs) is the increase of gate leakage current bydirect tunneling because the thickness of silicon dioxide (SiO₂) gateinsulators cannot be reduced further than about 1 nm. Silicon dioxidehas been used as a gate oxide material for decades. As transistors havedecreased in size, the thickness of the silicon dioxide gate dielectrichas steadily decreased to increase the gate capacitance and therebydrive current and device performance. As the thickness scales below 2nm, leakage currents due to tunneling increase drastically, leading tounwieldy power consumption and reduced device reliability. Replacing thesilicon dioxide gate dielectric with a high dielectric constant (high-k)material allows increased gate capacitance without the concomitantleakage effects.

Hafnium silicate and hafnium silicon oxynitride have been regarded assome of the most promising high-k materials to replace silicon dioxide.The inclusion of silicon and nitrogen theoretically prevents theformation and the diffusion of SiO gas at the high-k/substrateinterface. The most popular alternative to hafnium silicate and hafniumsilicon oxynitride has been HfAlO_(x) films.

Another approach is to form HfTaO_(x) films by alternative pulses (ALDmode) of a Hf precursor, H₂O (or another O source), a Ta precursor, H₂Oagain these pulses being separated by an appropriate purge by an inertgas (this sequence forms one cycle which will be typically repeatedseveral thousand times). As a result, the substrate surface is OHterminated after each H₂O pulse and the Hf or Ta precursors, ifsuitable, react with the surface in the following pulse. Nevertheless,tantalum suffers because of its very limited volatility. The mostpopular tantalum alkoxide, polyethylene terephthalate (PET) Ta(OEt)₅ isvolatile only above 130° C. However, for thin film depositionvaporization temperatures higher than 150° C. are generally required.The lack of volatility of these compounds is mainly due to the dimerstructure of the molecule. Using higher alkoxides will not lead to asignificantly more volatile molecule as an additional carbon atom oneach of the ligand would increase the molecular weight. As such, thereare no known solutions to adequately deposit HfTaO or HfTaON withchemical precursors using current deposition techniques such as chemicalvapor deposition (CVD), pulsed CVD or atomic layer deposition (ALD).

Consequently, there is a need for methods and compositions fordeposition of metal-TaO and/or metal-TaON for semiconductor fabrication.

BRIEF SUMMARY

Methods and compositions for depositing high-k films are disclosedherein. In general, the disclosed methods utilize precursor compoundscomprising Ta or Nb. More specifically, the disclosed precursorcompounds utilize certain ligands coupled to Ta and/or Nb such as1-methoxy-2-methyl-2-propanolate (mmp) to increase volatility.Furthermore, methods of depositing Ta or Nb compounds are disclosed inconjunction with use of Hf and/or Zr precursors to deposit Ta-doped orNb-doped Hf and/or Zr films. Other aspects of the methods andcompositions will be described in more detail below.

In an embodiment, a method for depositing a high-k film on to one ormore substrates comprises introducing a first metal precursor into thereaction chamber. The first metal precursor comprises a compound havingthe formula: M¹(OR)₄L¹. M¹ comprises Ta and Nb. R is an alkyl group, andL¹ has the formula, —O—(CR¹R²)_(n)—X—(R³)(R⁴) or—NR⁰—(CR¹R²)_(n)—X—(R³)(R⁴), where R⁰ is a hydrogen atom, or an alkylgroup having 1 to 4 carbon atoms. R¹ and R² may each independently be ahydrogen atom, a methyl group, or an ethyl group. The subscript “n” isan integer ranging from 0 and 3, X is an O or N atom. R³ is a hydrogenatom, or an alkyl group having from 1 to 4 carbon atoms, and R⁴ is ahydrogen atom, or an alkyl group having 1 to 4 carbon atoms. R⁰⁻⁴ may bethe same or different from one another. The first metal precursor mayadditionally comprise a compound having the formula:M¹(NR¹R²)(NR³R⁴)(NR⁵R⁶)(NR⁷R⁸)(NR⁹R¹⁰). M¹ comprises Ta or Nb. R⁰⁻¹⁰ mayeach independently be an alkyl group having from 1 to 6 carbon atoms,and R⁰⁻¹⁰ may be the same or different from one another. Moreover, thefirst metal precursor may be a compound having the formula:M¹(=NR⁰)(—NR¹R²)(—NR³R⁴)(—NR⁵R⁶), where R⁰⁻⁶ may each independently bean alkyl group having from 1 to 6 carbon atoms, and R⁰⁻⁶ may be the sameor different from one another. The first metal precursor may also be acompound having the formula: M¹(X)₅, S(R¹R²). M¹ is Ta or Nb. X is ahalogen, and R¹ and R² may each independently be an alkyl group having 1to 4 carbon atoms. The first metal precursor may further be anycombinations of the above compounds. The method further comprisesintroducing a second metal precursor into a reaction chamber. The secondmetal precursor comprises hafnium or zirconium. The reaction chambercontains the one or more substrates. In addition, the method comprisesvaporizing the first metal precursor and the second metal precursor todeposit the high-k film on to the one or more substrates.

In an embodiment, a precursor for the deposition of a high-k filmcomprises a compound having the formula: M¹(OR)₄L¹. M¹ comprises Ta andNb. R is an alkyl group, and L¹ has the formula,—O—(CR¹R²)_(n)—X—(R³)(R⁴) or —NR⁰—(CR¹R²)_(n)—X—(R³)(R⁴), where R⁰ is ahydrogen atom, or an alkyl group having 1 to 4 carbon atoms. R¹ and R²may each independently be a hydrogen atom, a methyl group, or an ethylgroup. The subscript “n” is an integer ranging from 0 and 3, X is an Oor N atom. R³ is a hydrogen atom, or an alkyl group having from 1 to 4carbon atoms, and R⁴ is a hydrogen atom, or an alkyl group having 1 to 4carbon atoms. R⁰⁻⁴ may be the same or different from one another. Theprecursor may also comprise a compound having the formula:M₁(NR¹R²)(NR³R⁴)(NR⁵R⁶)(NR⁷R⁸)(NR⁹R¹⁰). M¹ comprises Ta or Nb. R⁰⁻¹⁰ mayeach independently be an alkyl group having from 1 to 6 carbon atoms,and R⁰⁻¹⁰ may be the same or different from one another. Furthermore,the precursor may be a compound having the formula:M¹(=NR⁰)(—NR¹R²)(—NR³R⁴)(—NR⁵R⁶), where R⁰⁻⁶ may each independently bean alkyl group having from 1 to 6 carbon atoms, and R⁰⁻⁶ may be the sameor different from one another. In addition, the precursor may be acompound having the formula: M¹(X)₅, S(R¹R²). M¹ is Ta or Nb. X is ahalogen, and R¹ and R² may each independently be an alkyl group having 1to 4 carbon atoms. The first metal precursor may further be anycombinations of the above compounds.

The disclosed precursor compounds may have higher volatility thanexisting precursor compounds. Increased volatility expedites thedeposition of the high-k compounds as a film. The higher volatility isalso advantageous in process such as ALD because more volatileprecursors are easier to purge.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter that form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiments disclosed may be readily utilized as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. This document does not intendto distinguish between components that differ in name but not function.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . ”. Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect electrical connection. Thus, if a first device couples to asecond device, that connection may be through a direct electricalconnection, or through an indirect electrical connection via otherdevices and connections.

As used herein, the abbreviation “mmp” refers to1-methoxy-2-methyl-2-propanolate [OCMe₂CH₂OMe]. Further, theabbreviation “Me” refers to a methyl (CH₃—) group, the abbreviation “Et”refers to an ethyl (CH₄CH₂—) group, and the abbreviation “Bu” refers toa butyl group. The abbreviation “t-Bu” refers to a tertiary butyl group.

As used herein, the term “alkyl group” refers to saturated functionalgroups containing exclusively carbon and hydrogen atoms. Further, theterm “alkyl group” refers to linear, branched, or cyclic alkyl groups.Examples of linear alkyl groups include without limitation, methylgroups, ethyl groups, propyl groups, butyl groups, etc. Examples ofbranched alkyls groups include without limitation, t-butyl. Examples ofcyclic alkyl groups include without limitation, cyclopropyl groups,cyclopentyl groups, cyclohexyl groups, etc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an embodiment, a precursor for the deposition of high-k filmcomprises a compound having the formula: M¹(OR)₄L¹. M¹ may be a Group VBmetal. Preferably, M¹ is Ta or Nb. R is preferably an alkyl group suchas without limitation, Me or Et. However, R may be an alkyl group withany number of carbon atoms. L¹ is a chelating ligand or group forincreasing the volatility of the precursor for deposition purposes. Thechelating group may of the form —O—(CR¹R²)_(n)—X—(R³)(R⁴) or—NR⁰—(CR¹R²)_(n)—X—(R³)(R⁴) where R⁰ comprises hydrogen, or a alkylgroup having from 1 to 4 carbon atoms. The alkyl groups may be branched,linear, or cyclic. In addition, R¹ and R² may each independently be ahydrogen group, a methyl group, or an ethyl group. The subscript “n” maybe an integer ranging from 0 and 3. X is an O or N atom. R³ may be ahydrogen group, or a linear, cyclic or branched alkyl group having from1 to 4 carbon atoms. R⁴ may be a hydrogen group, or a linear, cyclic orbranched alkyl group having from 1 to 4 carbon atoms. R⁰⁻⁴ may be thesame or different from one another. According to one embodiment, theprecursor may be Ta(OMe)₄(mmp). Other examples of the precursor includewithout limitation, Nb(OMe)₄(mmp), Ta(OEt)₄(mmp), and Nb(OEt)₄(mmp).

The precursor may be prepared with any processes known to those of skillin the art. For example, Ta(OMe)₄(mmp) can be prepared from the additionof mmp-H to a stirred solution containing Ta(OMe)₅ (the molar ratiobetween Ta(OMe)₅ and mmpH may be 1:1). After stirring, the solution maybe set to reflux. The solvent may then removed in vacuo and the purecompound may obtained after vacuum distillation.

The precursor is designed so that embodiments of the precursor are morevolatile than existing Ta/Nb precursors such as dimeric Ta(OMe)₅ orTa(OEt)₅. Without being limited by theory, the disclosed precursors maybe more volatile than the dimeric precursors by promoting a monomericform. Accordingly, embodiments of the precursor are preferably liquid atroom or at moderate temperature (i.e. lower than vaporizationtemperature). Generally, embodiments of the precursor may have avaporization temperature ranging from about room temperature to about200 C alternatively from about 50 C to about 150 C.

In an alternative embodiment, the precursor may be a metal amide havingthe formula M¹(NR¹R²)(NR³R⁴)(NR⁵R⁶)(NR⁷R⁸)(NR⁹R¹⁰). M¹ is the same asdisclosed above (e.g. Ta, Nb, etc.). R¹⁻¹⁰ may each independently bemethyl or ethyl groups. Alternatively, embodiments of the precursor mayhave mixed amidoimido ligands such as M¹(=NR⁰)(—NR¹R²)(—NR³R⁴)(—NR⁵R⁶)where R⁰⁻⁶ may be linear, branched or cyclic alkyl groups having from 1to 6 carbon atoms. In specific embodiments, R⁰⁻⁶ may each independentlybe a methyl group or an ethyl group. R⁰⁻⁶ may be the same or differentfrom one another. In an exemplary embodiment, the precursor isTa(═N-t-Bu)(NEt₂)₃.

In yet another embodiment, the precursor may be a compound having theformula M¹(X)₅, S(R¹R²). M¹ may be a Group VB metal. Preferably, M¹ isTa or Nb. X is a halogen such as without limitation, Cl, Br, F, etc. R¹and R² may each independently be a linear, branched or cyclic alkylgroup having from 1 to 4 carbon atoms. R¹ and R² may be the same ordifferent from one another. In an exemplary embodiment, the precursormay be a TaCl₅, S(Et)₂ adduct.

The disclosed precursor compounds may be deposited using any depositionmethods known to those of skill in the art. Examples of suitabledeposition methods include without limitation, conventional CVD, lowpressure chemical vapor deposition (LPCVD), atomic layer deposition(ALD), pulsed chemical vapor deposition (P-CVD), plasma enhanced atomiclayer deposition (PE-ALD), or combinations thereof. In an embodiment, afirst metal precursor and a second metal precursor may be introducedinto a reaction chamber. The reaction chamber may be any enclosure orchamber within a device in which deposition methods take place such aswithout limitation, a cold-wall type reactor, a hot-wall type reactor, asingle-wafer reactor, a multi-wafer reactor, or other types ofdeposition systems under conditions suitable to cause the precursors toreact and form the layers.

Generally, the reaction chamber contains one or more substrates on towhich the high-k layers or films will be deposited. The one or moresubstrates may be any suitable substrate used in semiconductormanufacturing. Examples of suitable substrates include withoutlimitation, silicon substrates, silica substrates, silicon nitridesubstrates, silicon oxy nitride substrates, tungsten substrates, orcombinations thereof. Additionally, substrates comprising tungsten ornoble metals (e.g. platinum, palladium, rhodium or gold) may be used.

The first metal precursor may be any of the Ta/Nb precursors describedabove. The second metal precursor may be a compound having the formula:M²(L²)(L³)(L⁴)(L⁵). M² may be a Group IVB metal including withoutlimitation, Hf, Zr, etc. L²⁻⁵ may each independently be any suitablegroup including without limitation, a halogen, amide groups, alkoxidegroups, nitrate groups. In particular, suitable groups also includewithout limitation, Cl, NMeEt, NMe₂, NEt₂, NO3, or O-t-Bu. L²⁻⁵ may bethe same or different from on another. The ratio of the second metalprecursor to the first metal precursor introduced into the reactionchamber may range from about 100:1 to about 1:100, alternatively fromabout 1:1 to about 10:1.

In embodiments, the reaction chamber may be maintained at a pressureranging from about 0.1 Torr to about 1000 Torr. In addition, thetemperature within the reaction chamber may range from about 300° C. toabout 700° C. Furthermore, the deposition of the high-k film may takeplace in the presence of an oxidizing gas or an oxygen source. Examplesof suitable gases include without limitation, oxygen, ozone, hydrogenperoxide, nitric oxide, nitrous oxide, or combinations thereof. Inaddition, the deposition of the high-k film may take place in thepresence of a nitridizing (i.e. a nitrogen containing gas) gas such aswithout limitation, ammonia, hydrazine, substituted alkylhydrazines,amines, nitric oxide, nitrous oxide, or combinations thereof. It iscontemplated that both an oxidizing gas and a nitridizing gas may beintroduced into the reaction chamber. In further embodiments, an inertgas may be introduced into the reaction chamber. Examples of inert gasesinclude without limitation, He, Ar, Ne, or combinations thereof.

The first and second metal precursors may be introduced sequentially (asin ALD) or simultaneously (as in CVD) into the reaction chamber. In oneembodiment, the first and second metal precursors may be pulsedsequentially or simultaneously (e.g. pulsed CVD) into the reactionchamber while the oxidizing or nitridizing gas is introducedcontinuously into the reaction chamber. Each pulse of the first and/orsecond metal precursor may last for a time period ranging from about0.01 s to about 10 s, alternatively from about 0.1 s to about 5 s,alternatively from about 1 s to about 3 s. In another embodiment, theoxidizing gas and/or the nitridizing gas may also be pulsed into thereaction chamber. In such embodiments, the pulse of each gas may lastfor a time period ranging from about 0.01 s to about 10 s, alternativelyfrom about 0.1 s to about 5 s, alternatively from about 1 s to about 3s.

While embodiments of the invention have been shown and described,modifications thereof can be made by one skilled in the art withoutdeparting from the spirit and teachings of the invention. Theembodiments described and the examples provided herein are exemplaryonly, and are not intended to be limiting. Many variations andmodifications of the invention disclosed herein are possible and arewithin the scope of the invention. Accordingly, the scope of protectionis not limited by the description set out above, but is only limited bythe claims which follow, that scope including all equivalents of thesubject matter of the claims.

The discussion of a reference is not an admission that it is prior artto the present invention, especially any reference that may have apublication date after the priority date of this application. Thedisclosures of all patents, patent applications, and publications citedherein are hereby incorporated herein by reference in their entirety, tothe extent that they provide exemplary, procedural, or other detailssupplementary to those set forth herein.

What is claimed is:
 1. A precursor for depositing a high-k filmcomprising: a compound having the formula:M¹(OR)₄L wherein M¹ is selected from the group consisting of Ta and Nb,R is an alkyl group, and L has the formula —NR⁰—(CR¹R²)_(n)—N—(R³)(R⁴)wherein R⁰ is a hydrogen atom, or an alkyl group having 1 to 4 carbonatoms, R¹ and R² may each independently be a hydrogen atom, a methylgroup, or an ethyl group, n is an integer ranging from 0 to 3, R³ is ahydrogen atom, or an alkyl group having from 1 to 4 carbon atoms, and R⁴is a hydrogen atom, or an alkyl group having 1 to 4 carbon atoms andwherein R⁰⁻⁴ may be the same or different from one another.
 2. Theprecursor of claim 1 having a vaporization temperature less than 200° C.